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Hey guys, It seems that half the techs I ask say taking the superheat is useful for systems with expansion valves, and half say its for capilary systems. And I seem to get the same split response about subcooling. I work mostly residential. Whats the right answer?

Originally posted by newoldtech Hey guys, It seems that half the techs I ask say taking the superheat is useful for systems with expansion valves, and half say its for capilary systems. And I seem to get the same split response about subcooling. I work mostly residential. Whats the right answer?

Happy New year!
Adam

They are important in both systems , from my point of view anyway
each system is mainly designed with subcooling , but to get the subcooling right you have to get the superheat right too.

The primary function of the design engineer is to make things difficult for the fabricator and impossible for the serviceman.

Originally posted by newoldtech Hey guys, It seems that half the techs I ask say taking the superheat is useful for systems with expansion valves, and half say its for capilary systems. And I seem to get the same split response about subcooling. I work mostly residential. Whats the right answer?

Happy New year!
Adam

Taking the measurements is useful for any type of system, to identify trouble spots.

With txv still want to check superheat depending on sytem working on around 5-15 degrees superheat. But subcooling is going to tell if you have refrigerant issue in system with a txv.
Working residential units lennox has a different method to check they use subcooling on piston orfices to check there system charge. Most other units use superheat to adjust charge but i always check both so u know how the whole system is operating properly.

Hey try this on for size.
capped tube system.
wet bulb temp @ mixed return air * 3 - 80 - outdoor ambient /2
that is w/b * 3 -80 - odb / 2.
ex. 62*3-80-90/2 = 8 degrees superheat.
I got this formula off of this site over a year ago. It is as accurate as the manufacturers data plate stamped on the outdoor unit door. If you do have a txv metering system, you must charge by subcooling. You should always check both s/h & s/c on any system but you can expect 8-12 degrees superheat on a properly working txv system always. This is where your subcooling comes in. The more refrig. you add the more subcooling you will see.